1. Technical Field
The present invention relates to a four color display device and a method of converting an image signal thereof.
2. Related Art
Recently, an organic light emitting display device and a flat panel display have been actively developed. Such a flat panel display typically displays images based on three primary colors of red, green, and blue, and a white pixel may be added for the purpose of luminance enhancement. Such a four color flat panel display converts three input color image signals into four color image signals and displays an image based on the converted signals.
There are several methods of converting the three color image signals into the four color image signals. One of the methods converts each of the three color input image signals into luminance signals, defines a minimum value among values of the three luminance signals as a value of a white luminance signal, and then subtracts the minimum value from each of the three luminance signals. The four luminance signals are back-converted into image signals, thereby forming four color image signals.
However, a white pixel of a four color organic light emitting display device includes a white organic emission layer. A color coordinate of white light emitted from a white organic emitting layer made of a conventionally used material is biased to green at a low luminance. In other words, a greenish phenomenon of a low-luminance white may be shown, which may degrade the displayed image.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.